There have been many proposals in the literature for such compositions. In general they comprise a viscous or solid radiation-curable ethylenically unsaturated macromolecular or resinous e.g. oligomer or polymer component dissolved or dispersed in a liquid diluent comprising one or more ethylenically unsaturated monomers which are capable of copolymerising with the resinous component.
To be commercially acceptable as an adhesive for bonding glass in large scale manufacturing operations such as the manufacture of laminated glass products, the compositions must not only bond adequately in the cured state to the glass and to the other substrate, which may or may not be glass, but must also have an adequate shelf life and yet be able to be cured rapidly when exposed to the chosen irradiation, and must be available in a form having a viscosity sufficiently low in the uncured state to permit its facile application to a substrate in a thin and uniform layer without the need for sophisticated equipment.
For the production of laminated glass products intended to be used as windows or doors or in vehicles, the cured product from the composition must also be clear, colourless and transparent, preferably have a refractive index at least close to that of glass, exhibit adequate water- or moisture-resistance and be resistant to aging in sunlight. Further, since for many intended end uses it is desirable that at least one of the layers of the laminate is an organic glass such as methacrylate or polycarbonate or that a plastics foil such as of vinyl chloride polymer be provided between two glass sheets (one or both of which may be of organic glass), it is also desirable for the composition to bond well to certain plastics materials, especially those that are available as transparent sheets or film.
Much effort has been expended over the last 10-15 years in developing suitable compositions and a very wide variety of resinous components and diluent compositions has been proposed. One group of resins that has attracted particular interest comprises those which contain urethane groups and particular examples of these are the compounds obtainable by reacting a polyol with a polyisocyanate to form a preferably oligomeric urethane intermediate having terminal hydroxy and/or isocyanate groups and reacting the intermediate with an .alpha..beta.-ethylenically unsaturated compound having a group which is reactive with a hydroxy or isocyanate group as appropriate. Where the unsaturated compound contains a carboxylic group attached to a carbon atom of the .alpha..beta.-ethylenically unsaturated group i.e., contains the group ##STR1## product is called, for ease of reference, a urethane acrylate.
One class of composition that has shown particular promise as an adhesive for glass contains a preferably oligomeric urethane acrylate as the macromolecular component, or resin, and a reactive diluent such as acrylic acid, e.g. as described in European Patent publication No. 10355. However, for use in the production of safety laminates it would be desirable to improve the performance under impact of laminates formed using the composition as an adhesive and in particular to improve the retention in the laminate of glass splinters and fragments formed when a glass layer of the laminate is shattered. Of course, such increase should be obtained without unacceptable deterioration of other properties, particularly clarity, colour, water-resistance and resistance to ultra-violet light of the cured product and viscosity and stability of the uncured material.